Method and apparatus for estimating a downhole fluid property using a rare earth doped laser

ABSTRACT

A method and apparatus are disclosed for estimating a property of a downhole fluid, the apparatus including but not limited to a carrier that is conveyable in a borehole; a test cell carried by the carrier for capturing the downhole fluid; a rare earth doped electromagnetic energy source in electromagnetic energy communication with the downhole fluid in the test cell; and an electromagnetic energy detector in electromagnetic energy communication with electromagnetic energy emitted by the rare earth doped electromagnetic energy source that has interacted with the fluid for estimating the property of the downhole fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

None

Not Applicable

BACKGROUND

1. Technical Field

The present disclosure generally relates to well bore tools and in particular to an apparatus and methods for downhole spectrometry.

2. Background Information

Oil and gas wells have been drilled at depths ranging from a few thousand feet to as deep as 5 miles. Wireline and drilling tools often incorporate various sensors, instruments and control devices in order to carry out downhole operations. These operations may include formation testing, fluid analysis, and tool monitoring and control. In the oil and gas industry, formation testing tools have been used for monitoring formation pressures along a wellbore in a hydrocarbon bearing formation or reservoir, obtaining formation fluid samples from the wellbore and predicting performance of the reservoirs around the wellbore. Such formation testing tools typically contain an elongated body having an elastomeric packer that is sealingly urged against the zone of interest in the wellbore to collect formation fluid samples in storage test cells placed in the tool.

During drilling of a wellbore, a drilling fluid (“mud”) is used to facilitate the drilling process and to maintain a pressure in the wellbore greater than the fluid pressure in the formations surrounding the wellbore. This is particularly important when drilling into formations where the pressure is abnormally high. If the fluid pressure in the borehole drops below the formation pressure, there is a risk of blowout of the well. As a result of this pressure difference, the drilling fluid penetrates into or invades the formations for varying radial depths (referred to generally as invaded zones) depending upon the types of formation and drilling fluid used. The formation testing tools retrieve formation fluids from the desired formations or zones of interest, test the retrieved fluids to ensure that the retrieved fluid is substantially free of mud filtrates, and collect such fluids in one or more test cells associated with the tool. The collected fluids are brought to the surface and analyzed to determine properties of such fluids and to determine the condition of the zones or formations from where such fluids have been collected.

SUMMARY

The following presents a general summary of several aspects of the disclosure in order to provide a basic understanding of at least some aspects of the disclosure. This summary is not an extensive overview of the disclosure. It is not intended to identify key or critical elements of the disclosure or to delineate the scope of the claims. The following summary merely presents some concepts of the disclosure in a general form as a prelude to the more detailed description that follows.

A method and apparatus are disclosed for estimating a property of a downhole fluid, the apparatus including but not limited to a carrier that is conveyable in a borehole; a test cell carried by the carrier for capturing the downhole fluid; a rare earth doped electromagnetic energy source in electromagnetic energy communication with the downhole fluid in the test cell; and an electromagnetic energy detector in electromagnetic energy communication with electromagnetic energy emitted by the rare earth doped electromagnetic energy source that has interacted with the fluid for estimating the property of the downhole fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed understanding of the present disclosure, reference should be made to the following detailed description of the several non-limiting embodiments, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:

FIG. 1 is a schematic diagram of a particular illustrative embodiment deployed on a wire line in a downhole environment;

FIG. 2 is a schematic diagram of another particular illustrative embodiment deployed on a drill string in a monitoring while drilling environment;

FIG. 3 is a schematic illustration of a particular illustrative embodiment according to the disclosure;

FIG. 4 is a schematic illustration of another particular illustrative embodiment according to the disclosure;

FIG. 5 is a schematic illustration of another particular illustrative embodiment according to the disclosure; and

FIG. 6 is a schematic illustration of another particular illustrative embodiment according to the disclosure.

DETAILED DESCRIPTION

The present disclosure uses terms, the meaning of which terms will aid in providing an understanding of the discussion herein. As used herein, high temperature refers to a range of temperatures typically experienced in oil production well boreholes. For the purposes of the present disclosure, high temperature and downhole temperature include a range of temperatures from about 100 degrees C. to about 290 degrees C. and above.

The term “carrier” as used herein means any device, device component, combination of devices, media and/or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and/or member. Exemplary non-limiting carriers include wire lines and drill strings of the coiled tube type, of the jointed pipe type and any combination or portion thereof.

A “downhole fluid” as used herein includes any gas, liquid, flowable solid and other materials having a fluid property. A downhole fluid may be natural or man-made and may be transported downhole or may be recovered from a downhole location. Non-limiting examples of downhole fluids include but are not limited to drilling fluids, return fluids, formation fluids, production fluids containing one or more hydrocarbons, oils and solvents used in conjunction with downhole tools, water, brine and combinations thereof.

“Processor” as used herein means any device that transmits, receives, manipulates, converts, calculates, modulates, transposes, carries, stores or otherwise utilizes data. In several non-limiting aspects of the disclosure, a processor includes but is not limited to a computer that executes programmed instructions stored on a tangible non-transitory computer readable medium for performing various methods.

Q as used herein is a dimensionless parameter that describes how under-damped an oscillator or resonator is, or equivalently, characterizes a resonator's bandwidth relative to its center frequency. Higher Q indicates a lower rate of energy loss relative to the stored energy of the oscillator; the oscillations die out more slowly. A pendulum suspended from a high-quality bearing, oscillating in air, has a high Q, while a pendulum immersed in oil has a low one. Oscillators with high quality factors have low damping so that they ring longer. The optical Q is equal to the ratio of the resonant frequency to the bandwidth of the cavity resonance. The average lifetime of a resonant photon in the cavity is proportional to the cavity's Q.

Portions of the present disclosure, detailed description and claims may be presented in terms of logic, software or software implemented illustrative embodiments that are encoded on a variety of tangible non-transitory computer readable storage media including, but not limited to tangible non-transitory computer readable media, program storage media or computer program products. Such media may be handled, read, sensed and/or interpreted by an information processing device. Those skilled in the art will appreciate that such media may take various forms such as cards, tapes, magnetic disks (e.g., floppy disk or hard disk drive) and optical disks (e.g., compact disk read only memory (“CD-ROM”) or digital versatile (or video) disk (“DVD”)). Any embodiment disclosed herein is for illustration only and not by way of limiting the scope of the disclosure or claims.

In a particular illustrative embodiment, a spectrometer is disclosed for estimating a property of a downhole fluid. In a particular embodiment, the spectrometer is used to estimate a property of a downhole fluid by detecting the presence of chemical components in the downhole fluid. In a particular embodiment, an optical pump laser is provided in the 600-1200 nanometer range to introduce electromagnetic energy into a rare earth doped laser. Non-limiting examples of the rare earth doped laser are a rare earth doped opal laser and a rare earth dope photonic crystal laser. Any laser may be used that is suitable in accordance with the disclosure. The lasing wavelength of the photonic crystal rare earth doped laser can be adjusted to emit electromagnetic energy suitable to detect several chemicals of interest in situ downhole in a downhole fluid. Such chemicals of interest may include but are not limited to C1 methane, C2 ethane, C3 propane, C4 butane and C5 pentane of H2S (hydrogen sulfide), H2S and CO2.

In a particular embodiment, an electro optic modulator (EOM) is provided to tune a frequency of electromagnetic energy emitted by a photonic crystal rare earth doped laser. An EOM is an optical device in which a signal-controlled element displaying electro-optic effect is used to modulate a beam of electromagnetic energy. The modulation may be imposed on the phase, frequency, amplitude, or polarization of the modulated beam. The EOM is used to apply a change in stress or temperature to the photonic crystal rare earth doped laser to change the frequency of electromagnetic energy emitted by the laser to scan for several wavelengths of interest. In another particular embodiment a plurality of lasers, which can be photonic crystals, each having a separate wavelength, are used to provide several different wavelengths.

Photonic crystal lasers are composed of periodic dielectric or metallo-dielectric nanostructures that affect the propagation of electromagnetic waves (EM) in the same way as the periodic potential in a semiconductor crystal affects the electron motion by defining allowed and forbidden electronic energy bands. Essentially, photonic crystals contain regularly repeating internal regions of high and low dielectric constant. Photons (behaving as waves) propagate through this structure—or not—depending on their wavelength. Wavelengths of electromagnetic energy that are allowed to travel are known as modes, and groups of allowed modes form bands.

Disallowed bands of wavelengths are called photonic band gaps. This gives rise to distinct optical phenomena such as inhibition of spontaneous emission, high-reflecting omni-directional mirrors and low-loss-wave guiding, amongst others. It is essentially a natural photonic crystal, although it does not have a complete photonic band gap. The opal is a natural periodic microstructure responsible for its iridescent color. The most frequently used laser-active rare earth ions and host media together with typical emission wavelength ranges are shown in the Table 1.

TABLE 1 Common Laser-Active Rare Earth Ions And Host Media And Example Emission Wavelengths Example Emission Ion Name Common Host Media Wavelengths neodymium (Nd³⁺) YAG, YVO₄, YLF, 1.03-1.1 μm, 0.9-0.95 μm, silica 1.32-1.35 μm ytterbium (Yb³⁺) YAG, tungstates, silica 1.0-1.1 μm erbium (Er³⁺) YAG, silica 1.5-1.6 μm, 2.7 μm, 0.55 μm thulium (Tm³⁺) YAG, silica, fluoride 1.7-2.1 μm, 1.45-1.53 μm, glasses 0.48 μm, 0.8 μm holmium (Ho³⁺) YAG, YLF, silica 2.1 μm, 2.8-2.9 μm praseodymium silica, fluoride glasses 1.3 μm, 0.635 μm, 0.6 μm, (Pr³⁺) 0.52 μm, 0.49 μm cerium (Ce³⁺) YLF, LiCAF, LiLuF, 0.28-0.33 μm LiSAF, and similar fluorides

Ytterbium- and neodymium-doped gain media for lasers and erbium-doped fibers for erbium-doped fiber amplifiers. Other rare-earth-doped ions are yttrium (Y³⁺), samarium (Sm³⁺), europium (Eu³⁺), gadolinium (Gd³⁺), terbium (Tb³⁺), dysprosium (Dy³⁺), and lutetium (Lu³⁺) which are also used sometimes as a codopant, e.g. for quenching the population in certain energy levels by energy transfer processes, or for realizing saturable absorbers, or as optically passive constituents of laser crystals.

There is a wide range of crystalline media (laser crystals) which can serve as host media for laser-active rare earth ions. Frequently used crystal materials are certain oxides (e.g. YAG), vanadates (YVO₄, GdVO₄), tungstates (KGW, KYW), fluorides (YLF, CaF), borates (BOYS), and apatites (S-FAP, SYS). Numerous scholarly articles on gain media and laser crystals discuss a number of important properties of host crystals. Compared with crystals, rare-earth-doped glasses usually allow for a larger gain bandwidth and thus larger wavelength tuning ranges, and also shorter ultra-short pulses with passive mode locking. Such glasses are used in the form of bulk pieces or optical fibers (e.g. rare-earth-doped silica fibers). The high optical confinement in fibers allows operation even on “difficult” laser transitions with low gain efficiency. Special fibers, e.g., fibers made on fluoride glass have particularly low phonon energies, leading to good mid-infrared transmission and long metastable level lifetimes. They are also often used for up conversion lasers. Numerous scholarly articles are also available on rare-earth-doped fibers, laser crystals versus glasses, and ceramic gain media.

Rare-earth-doped gain media have in common that the pump and laser transitions are so-called “weakly allowed transitions” with fairly small oscillator strength. A consequence of this is that the upper-state lifetimes of a range of microseconds to milliseconds, so that substantial amounts of energy can be stored in such media. Depending on the phonon energies of the host medium, some of the level lifetimes can be strongly quenched by multi-phonon transitions. Such effects are minimized in low-phonon-energy host media such as fluoride fibers. Quenching effects can be welcome if they depopulate the lower laser level, thus preventing or reducing reabsorption, or if they help to populate the upper laser level within the pumping process. Various kinds of interactions, in particular dipole-dipole interactions, allow energy transfer between different rare earth ions either of the same species or of different species. This is exploited e.g. in erbium-ytterbium-co doped fibers, where the pump radiation is dominantly absorbed by ytterbium ions and mostly transferred to erbium ions.

Turning now to FIG. 1, FIG. 1 is a schematic representation of a wireline formation testing system 100 for estimating a property of a downhole fluid. FIG. 1 shows a wellbore 111 drilled in a formation 110. The wellbore 111 is shown filled with a drilling fluid 116, which is also is referred to as “mud” or “wellbore fluid.” The term “connate fluid” or “natural fluid” herein refers to the fluid that is naturally present in the formation, exclusive of any contamination by the fluids not naturally present in the formation, such as the drilling fluid. Conveyed into the wellbore 111 at the bottom end of a wireline 112 is a formation evaluation tool 120 that includes but is not limited to an analysis module 150 and a spectrometer 121 made according to one or more embodiments of the present disclosure for in-situ estimation of a property of the fluid withdrawn from the formation. The formation evaluation tool 120 acts a carrier for the spectrometer 121 and a sample tank 122 also referred to herein as a test cell. Exemplary embodiments of various spectrometers are described in more detail in reference to FIGS. 3-6. The wireline 112 typically is an armored cable that carries data and power conductors for providing power to the tool 120 and a two-way data communication link between a tool processor in the analysis module 150 and a surface controller 140 placed in surface unit, which may be a mobile unit 131, such as a logging truck. The surface controller 140 and analysis module 150 each may include but are not limited to a processor 130, data interface 132 and non-transitory computer readable media 134.

The wireline 112 typically is carried from a spool 115 over a pulley 113 supported by a derrick 114. The controller 140 and analysis module 150 are each in one aspect, a computer-based system, which may include one or more processors such as a microprocessor, that may include but is not limited to one or more non-transitory data storage devices, such as solid state memory devices, hard-drives, magnetic tapes, etc.; peripherals, such as data input devices and display devices; and other circuitry for controlling and processing data received from the tool 120. The surface controller 140 and analysis module 150 may also include but are not limited to one or more computer programs, algorithms, and computer models, which may be embedded in the non-transitory computer-readable medium that is accessible to the processor for executing instructions and information contained therein to perform one or more functions or methods associated with the operation of the formation evaluation tool 120. Thus processing may occur at the surface particular embodiment, or in situ in other embodiments. Processing may be split between the surface and in situ in other embodiments.

The test cell may include but is not limited to a downhole fluid sample tank 122 and a flow line 211 (shown in FIG. 2) through which downhole fluid flows into the downhole fluid sample tank 122. The test cell may be any suitable downhole fluid receptacle in accordance with the disclosure. At least a portion of the spectrometer 121 is immersed in the downhole fluid in the test cell and used for in situ or surface analysis of the downhole fluid, including but not limited to estimating a property of the downhole fluid. Additional downhole test devices for estimating a property of the downhole fluid may be included in the formation evaluation tool 120. Any test device may be included in accordance with disclosure, including but not limited to nuclear magnetic resonance (NMR) spectrometers, pressure, temperature, optomechanical resonators and electromechanical resonators for estimating density and viscosity of a downhole fluid.

FIG. 2 depicts a non-limiting example of a drilling system 200 in a measurement-while-drilling (MWD) arrangement according to one embodiment of the disclosure. A derrick 202 supports a drill string 204, which may be a coiled tube or drill pipe. The drill string 204 may carry a bottom hole assembly (BHA) 220 and a drill bit 206 at a distal end of the drill string 204 for drilling a borehole 210 through earth formations. Drilling operations according to several embodiments may include pumping drilling fluid or “Mud” from a mud pit 222, and using a circulation system 224, circulating the mud through an inner bore of the drill string 204. The mud exits the drill string 204 at the drill bit 206 and returns to the surface through an annular space between the drill string 204 and inner wall of the borehole 210.

In the non-limiting embodiment of FIG. 2, the BHA 220 may include a formation evaluation tool 120, a power unit 226, a tool processor 212 and a surface controller 140. Any suitable power unit may be used in accordance with the disclosure. Non-limiting examples of suitable power units include but are not limited to a hydraulic, electrical, or electro-mechanical and combinations thereof. The tool 120 may carry a fluid extractor 228 including a probe 238 and opposing feet 240. In several embodiments to be described in further detail below, the tool 120 includes but is not limited to a downhole spectrometer system 121. A flow line 211 connects fluid extractor 228 to sample tank 122 and spectrometer 121. Downhole fluid flows from the formation into the sample tank from fluid extractor through the flow line into the sample tank. The spectrometer may be used in either the while-drilling embodiments or in the wireline embodiments for in situ or surface estimation of a property of the downhole fluid.

Those skilled in the art with the benefit of the present disclosure will recognize that the several embodiments disclosed are applicable to a downhole fluid production facility without the need for further illustration. The several examples described below and shown in FIG. 3-6 may be implemented using a wireline system as described above and shown in FIG. 1, may be implemented using a while-drilling system as described above and shown in FIG. 2 or may be implemented in a production facility to monitor production fluids.

FIG. 3 shows a schematic diagram of a module of the spectrometer 121 for use in a downhole tool, such as the tool 120. It is shown to include certain elements or components of the spectrometer 121 made according to one exemplary embodiment. A portion 331 of the downhole fluid entering the tool 120 is passed into or through sample tank flow line 221 to the test cell shown as sample tank 122 as a downhole fluid. The test cell could also be the fluid flow line 211. The term “test cell” as used herein is used to synonymously refer to the sample tank flow line 211 and the sample tank 122 both of which contain downhole fluid. The test cell, in one aspect, may include a first window 334 for ingress and egress of electromagnetic energy into downhole fluid 331 in the test cell. Electromagnetic energy is emitted from a source 310. In a particular embodiment, a second window 336, generally on the opposite side of the first window, for allowing electromagnetic energy to pass out of the fluid. The test cell may hold the downhole fluid or may allow it to pass there through.

An electromagnetic energy pump 310, in one particular illustrative embodiment, may be a laser pump that emits electromagnetic energy 301 introduced to the electromagnetic energy source, 342 which can be a laser that emits electromagnetic energy. The electromagnetic energy emitted by the electromagnetic energy source, is labeled 303 a as it travels from the electromagnetic energy source to the downhole fluid 331 through the first window 334. The Electromagnetic energy emitted by the electromagnetic energy source is labeled 303 b after it passes through the downhole fluid 331 and out of the window 336 after interacting with the downhole fluid 331. The interaction of the electromagnetic energy 303 a with the fluid may include absorption and/or scattered and reflected electromagnetic energy 304 of the electromagnetic energy 303 a. The electromagnetic energy source 342 in on one non-limiting embodiment can be a laser.

In other embodiments, the electromagnetic energy source can be any electromagnetic energy source in accordance with the disclosure. In another embodiment the electromagnetic energy source 342 is an array of lasers that includes a number of lasers 342 a-342 n that may include but are not limited to a plurality of rare earth doped photonic crystals 342 a-342 n, wherein each rare earth doped photonic crystal is tuned by doping the photonic crystal laser with a particular rare earth element to provide electromagnetic energy output 303 corresponding to a distinct wavelength. Each photonic crystal laser 342 a-342 n in the laser array may be designated to correspond to a spectrometric analysis channel at a particular frequency in the spectrometer. In another particular embodiment, an electromagnetic energy spectrum of interest may range from ultraviolet wavelength to infrared wavelength. The electromagnetic spectrum may be divided into a desired number of relatively narrow wavelength bands, each wavelength band having a particular center wavelength. Each such band may correspond to output electromagnetic energy from a separate photonic crystal. The electromagnetic energy source 342 may include a fluorescent source that passes fluorescent electromagnetic energy into the downhole fluid.

In a particular illustrative embodiment, each laser is a doped silicon wafer fabricated to contain a specific pattern of air spaces in a suitable semiconductor material such that each laser 342 a-342 n is tuned to provide output electromagnetic energy that corresponds to a specific center wavelength. In particular illustrative embodiment, the total number of lasers may correspond to the total number of channels that comprise the desired spectrum of the spectrometer. For example, if the spectrum of interest ranges from 200 nm to 2500 nm and the total desired channels equal fifty, then fifty photonic crystals may be tuned to cover the entire chosen spectrum. In another particular illustrative embodiment, a number of photonic crystal channels are packed into a relatively small space by using photonic crystal optical fibers. Such fibers, in one aspect, may contain many elongated air holes parallel to the fiber axis that run the length of the fiber. Such fibers are sometimes referred to as “holey fibers.”

In another particular illustrative embodiment, a group of lasers which may be rare earth doped photonic crystals may be tuned to different wavelengths of interest. For example, a particular photonic crystal may be tuned to emit electromagnetic energy transmitted through the fluid that corresponds to a particular wavelength band where the refractive index or absorption is of interest, such as for oil, water, gas, etc. In one aspect, each laser, which in a particular embodiment is a rare earth dope photonic crystal may be configured to contain a unique pattern of air spaces in a substrate (such as solid-state substrate) to provide output electromagnetic energy corresponding to a particular wavelength. The array of lasers, which in a particular embodiment are photonic crystals, may be housed in one or more common modules for use in the tool downhole. The modules, when desired, may be placed inside a cooling test cell, such as a flask or may be cooled using another cooling device, such as a sorption cooler, cruogenic cooler or thermoelectric cooler. In another particular illustrative embodiment the photonic crystals or other laser types are provided with a thermal device 333 to thermally adjust the frequency of each of the laser's electromagnetic energy output. Non-limiting examples of the thermal device 333 include but are not limited to a Dewar cooling flask and a resistive heater. Any thermal device made in accordance with the disclosure is suitable.

In another particular illustrative embodiment, an EOM 333 is provided to tune or change the frequency of electromagnetic energy out put by the laser 342. The laser may be any suitable type tunable laser including but not limited to the lasers described herein. In a particular embodiment, an EOM applies thermal energy to the laser to change the frequency of the electromagnetic energy emitted by the laser. In another embedment the EOM applies mechanical stress from a mechanical or piezoelectric device to change the frequency of the electromagnetic energy emitted by the laser. In a particular embodiment the EOM is integrated on a silicon wafer with the laser for control of each of the laser's output electromagnetic energy wavelength. In another illustrative embodiment, the EOM applies thermal energy or stress to more than one laser at a time to tune the lasers in groups of 2 or more. In another illustrative embodiment, the EOM tunes each laser in a group of lasers one at a time individually.

Electromagnetic energy from each photonic crystal laser may be detected by a common or separate photo detector 346. For example, a single photo detector 346 or an array of photo detectors 346 a-346 n may be used to detect electromagnetic energy from a corresponding laser 342 a-342 n. An interface circuit in processor 132 receives a measurement of electromagnetic energy from the photo detectors 346 a-346 n, converts the received measurement of electromagnetic energy into digital signals and provides the digital signals to a controller 358. The controller 358 may include a processor 130, which may be a microprocessor, a set of computer programs stored in a non-transitory computer readable medium 134 that is in data communication with the processor 130. The processor processes the data received from the photodetector 346 to estimate a property of the downhole fluid. The controller may be disposed in the downhole tool or at the surface. Alternatively, the data may be processed to a certain extent downhole by a first controller 358 deployed in the tool and the remaining processing may be accomplished at the surface by another suitable controller, such as controller 140 (FIG. 1). Data communication between a downhole controller and the surface controller may be managed via any suitable telemetry link, such as a data link from processor data interface 132 in controller 358, 310 to surface controller 140. The data link may be any suitable data transmission medium in accordance with the disclosure, including but not limited to a wireline, wired pipe, mud pulse telemetry, acoustic telemetry, and electromagnetic telemetry, etc.

Electromagnetic energy that has interacted with the fluid passes through windows 336 and 334. Electromagnetic energy that passes through window 336 is received by photo detector 346 which may be an array of photo detectors 346 a-346 n.

A UV laser or another suitable electromagnetic energy source 310 is used to introduce electromagnetic energy to laser 342 which emits electromagnetic energy 303 a through window 334 to downhole fluid 331. In a particular embodiment, electromagnetic energy is pumped by the laser pump within a relatively narrow UV wavelength band tuned to produce monochromatic (substantially single wavelength) UV electromagnetic energy. The electromagnetic energies 303 b and 304 that have interacted with the fluid 331 are detected by the photo detector modules 346 and/or 347 respectively. Photo detectors 346 and 347 may each be a singular or plurality of photo detectors in an array of photo detectors as discussed above regarding photo detector 346. In a particular embodiment, the photodetector array includes but is not limited to an array of photonic crystals tuned to pass a selected spectrum of electromagnetic energy and provide such spectrum to the processor 130 for analysis. Alternatively, electromagnetic energy reflected 304 from the fluid may be detected for estimating a property of the downhole fluid. Such a system may be utilized to obtain Raman scattering for estimating in-situ a property of the fluid 331. Processor 130 executes computer program instructions stored in computer readable memory 134 on controller 358.

Continuing with the example of FIG. 3, the electromagnetic energy emitted from the electromagnetic energy source 310 or array 342 may be modulated by a processor 130 within the same controller 358 that receives the photodetector output or by a separate modulator in a second controller 315 including but not limited to a processor, computer readable medium and data interface (not shown for simplicity). In the example shown in FIG. 3, one controller 358 is in data communication with the photodetector 334 and a second controller 315 is in data communication with the EOM 333 for modulating electromagnetic energy emitted by the electromagnetic energy source 310 or the array 342 respectively. These controllers may be implemented as a single controller downhole without departing from the scope of the disclosure. In other embodiments, the controller or controllers may be located at the surface of the well borehole.

In wireline embodiments, communication may be accomplished via the wireline cable. In while-drilling embodiments, communication may be accomplished via wired pipe, acoustic pipe communication, or by mud-pulse telemetry. In wireline embodiments disclosed herein, the electromagnetic energy source 310 or array 342 may be located at a well borehole surface location and the electromagnetic energy path may include one or more optical fibers extending from the surface location to the downhole tool using the wireline cable as a support.

In one particular embodiment, the electromagnetic energy source 310 or laser array 342 may include one or more electromagnetic energy emitting semiconductors used as the individual electromagnetic energy sources 342 a-342 n. For example, the one or more electromagnetic energy sources 342 and 342 a-342 n may include one or more rare earth doped laser fibers, rare earth doped laser wafers, rare earth doped silicon on insulator lasers, which may include one or more ridge waveguide quantum cascade lasers, one or more buried hetero structure waveguide quantum cascade lasers (QCL), one or more Fabry Perot quantum cascade lasers, one or more distributed feedback (“DFB”) quantum cascade lasers, one or more distributed Bragg reflector (“DBR”) quantum cascade lasers, or any combination thereof. As used herein, “QCL,” refers generally to quantum cascade lasers, types of which may include but are not limited to ridge waveguide quantum cascade lasers, buried hetero structure waveguide quantum cascade lasers, Fabry Perot quantum cascade lasers, DFB quantum cascade lasers and DBR quantum cascade lasers. Quantum cascade lasers exhibit relatively narrow line widths and are wavelength tunable. The individual electromagnetic energy sources may be operated continuously or in a pulsed mode to emit an electromagnetic energy of a selected wavelength or wavelengths toward the downhole fluid in the test cell. In several non-limiting embodiments, the individual electromagnetic energy sources can emit electromagnetic energy in the infrared region. The wavelength of lasers may be changed such that the derivative of the spectra may be measured which can remove the requirement for background calibration.

Multiple wavelengths of electromagnetic energy emitted by lasers arranged in an array may be detected using a single photodetector. Photo detectors typically experience drift with respect to another as temperature increases, meaning that the response characteristics of each photodetector is unique when subjected to temperature fluctuations. Using a single photodetector reduces the need to account for differences in how one photodetector drifts with respect to other photo detectors.

Each laser 342 a-342 n in the array 342 can be configured or selected to emit an electromagnetic energy having a wavelength corresponding to a different optical channel of the spectrometer 121. In one embodiment, modulating the electromagnetic energy sources includes turning each electromagnetic energy source on individually and sequentially using the controller 315 and EOM 333 so that each electromagnetic energy source in the array 342 emits a specific wavelength of electromagnetic energy through the fluid 331 in test cell at a different time. In another embodiment, each source in the array emits at the same time. In a particular embodiment, each laser in array 342 can be tuned individually or in a group of two or more by EOM 333.

Maintaining the at least one electromagnetic energy source at a constant temperature helps to provide wavelength stability. In one embodiment, the electromagnetic energy source array is maintained at a substantially constant temperature by thermal device 313. In another embodiment the wavelength of each electromagnetic energy source is modulated by rapidly changing its temperature over a small temperature range. This rapid temperature change can be accomplished by rapidly changing the current through the electromagnetic energy source or by changing electrical current supplied to auxiliary resistive heaters in thermal contact with each electromagnetic energy source. In another embodiment the wavelength is modulated by using an external cavity. Alternatively, each electromagnetic energy source's wavelength could be modulated using EOM 333 to modulate the electromagnetic energy source's temperature, which is done most easily by modulating the current through it or by providing a heater or stressor (piezoelectric or mechanical) adjacent the electromagnetic energy source to modulate the frequency of electromagnetic energy out put. The frequency modulation enables performance of derivative spectroscopy with helps to find small peaks on an amplitude spectrum curve.

In another embodiment, the wavelength of each laser 342 a-342 n may be modulated to each emit a different frequency, which saves time through the multiplexing advantage associated with measuring all wavelengths simultaneously with a single photodetector. Then, the output of the photodetector can be filtered (digitally or in hardware) to recover that portion of the photodetector response that is the result of any particular laser.

Turning now to FIG. 4, FIG. 4 is a schematic diagram of a portion of another particular illustrative embodiment of a spectrometer 121 for estimating a property of the downhole fluid in a downhole tool, such as tool 120 shown in FIGS. 1 and 2. The spectrometer 121 includes an electromagnetic energy pump 310 such as described above. The laser array 342 is immersed in downhole fluid inside of the test cell and is in electromagnetic communication with electromagnetic energy pump 310 and photo detectors 346 and 347. In one embodiment the lasers are a rare earth doped photonic crystal module 342 containing a number of tuned photonic crystals 342 a-342 n. Each of the tuned photonic crystals receives the electromagnetic energy 301 from the laser pump and provides as output electromagnetic energy 303 that corresponds to a desired respective wavelength. A photo detector 346 senses the output band of each of the photonic crystals 342-342 n. Electromagnetic energy output 303 from the photonic crystals then passes through the fluid 331 and is received by a photodetector 346, which converts the received electromagnetic energy to electrical signals that pass to the controller 358 for processing.

In another illustrative embodiment, the electromagnetic energy source 342 is a miniature laser such as a rare earth doped nanocavity laser. The high-Q nanocavity laser is miniature and can be located inside of the test cell and immersed in the fluid as shown in FIG. 4 or outside of the test cell as shown in FIG. 3. High Q indicates a Q of about 1,000 and higher.

As shown in FIG. 4, one particular example of a spectrometer 121 includes but is not limited to an electromagnetic energy source array 342 of individual electromagnetic energy sources 342 a-342 n positioned inside of test cell. The array 342 of this non-limiting example includes multiple electromagnetic energy sources producing infrared electromagnetic energy, for example mid-infrared electromagnetic energy, within a relatively narrow wavelength band. Alternatively, the electromagnetic energy source array 342 may produce multiple monochromatic (single wavelength) infrared electromagnetic energy from each electromagnetic energy source 342 a-342 n. The infrared electromagnetic energy 303 a interacts with the fluid 331 and at least a portion of the electromagnetic energy is reflected back to an electromagnetic energy detector 347. In the current non-limiting example the electromagnetic energy source is a laser and the electromagnetic energy detector is a photodetector. Any electromagnetic energy source and electromagnetic energy detector in accordance with the disclosure may be used in other embodiments. The photodetector 347 produces a signal responsive to the electromagnetic energy, which signal is received by a processor 130 for analysis. In a particular embodiment, the photodetector 347 may be any photodetector that can detect spectra of Raman scatters corresponding to the electromagnetic energy emitted from at least one of the lasers 342 a-342 n. The processor 130 may further be used as a modulator for the at least one electromagnetic energy source 310 to modulate the electromagnetic energy emitted from the electromagnetic energy pump 310.

The photodetector signals are passed to the controller 358, which may include a processor 130, and memory for storing data and computer programs in a computer readable medium 134. The controller 358 receives and processes the signals received from the detector 346. In one aspect, the controller 358 may analyze or estimate the detected electromagnetic energy and transmit a spectrum of the Raman scattered electromagnetic energy to a surface controller using a transmitter 358. In one aspect, the controller 358 may estimate one or more properties of the downhole fluid and transmit the results to a surface controller using a transmitter (not shown). In another aspect, the controller 358 may process the signals received from the detector 346 to an extent and telemeter the processed data to a surface controller for producing a spectrum and for providing an in-situ estimate of a property of the fluid, including the contamination level of the mud in the formation fluid. The spectrum provided by the Raman spectrometer 121 may be used to estimate, for example, oil-based mud contamination and relative components in crude oils of one or more compounds in the fluid sample, such as esters or olefins.

Turning now to FIG. 5, in another illustrative embodiment, an electromagnetic energy source 502 is inside the test cell and immersed in the fluid 331 and the property of the fluid is estimated from the surrounding medium refractive index (SRI). In a particular embodiment, the electromagnetic energy source is laser wave guide formed along a silicon wafer ridge which leaks electromagnetic energy from the wave guide into the downhole fluid 331. Any electromagnetic energy source suitable for estimating a property of a fluid in accordance with the disclosure can be used. The electromagnetic energy leaked from the waveguide is reflected by the fluid in the test cell. Using SRI, a property of the fluid is determined. In the present example, the laser pump 310 is located out side of the test cell and provide electromagnetic energy to the electromagnetic energy source 502. In particular embodiment, the electromagnetic pump also receives the SRI response of the electromagnetic energy source for estimation of a property of the fluid. In another particular embodiment, the electromagnetic energy detector 346 receives the SRI response of the electromagnetic energy source for estimation of a property of the fluid.

Any electromagnetic energy source may be used for SRI in accordance with the disclosure. In a particular embodiment, a non-limiting example of the electromagnetic energy source 502 is a species-specific metal clad segment on the laser waveguide, which in a non-limiting example is a planar waveguide, allows controlled light leakage of light propagating through the laser waveguide by total internal reflection, to measure refractive index and identify chemical species in the downhole fluid. Any electromagnetic energy source electromagnetic energy source for use with reading an SRI of a downhole fluid in accordance with the disclosure is acceptable. In the current non-limiting exemplary embodiment, the laser waveguide 502 also acts as a sensor designed for a particular chemical species by selecting a metal clad with an affinity for the species and by matching the refractive indices of the laser waveguide body, clad, metal clad segment and chemical species. Dual or multiple measurement methods use a pair or multiple metal clad segments of different specificity. The metal clad segment may include another material to provide a suitable refractive index while having the desired affinity for the chemical species or to provide a catalyst to react the species to form a reaction product which is more readily detected.

Turning now to FIG. 6, in another particular embodiment, the electromagnetic energy source, which can be a laser array 342 a-342 n or an individual laser 342 is interrogated by electromagnetic energy source 310 which further comprises a filter 602 for a particular wavelength corresponding to a frequency indicative of a particular chemical for estimating a property of the downhole fluid. In a non-limiting embodiment, filter 602 further includes but is not limited to gratings 603, 604 and 605 each of which reflect a different frequency of electromagnetic energy 607, 608 and 609 from electromagnetic energy 404. In a particular embodiment, the electromagnetic energy reflected by filters 607, 608 and 609 are used to estimate a property to the downhole fluid by detecting different compounds of interest in the downhole fluid. In a particular embodiment, the channels of the spectrometer 121 are formed in part by gratings 603, 604 and 605.

The property of the fluid may be any desired property, including, but not limited to absorbance; refractive index; mud filtrate contamination; gas-oil ratio; oil-water ratio; gas-water ratio; an absorbance spectrum; reflectivity spectrum and a Raman spectrum. Additionally, a preprocessor associated with a controller may be located in a downhole portion of the apparatus, at the surface, or partially in the apparatus downhole and partly at the surface. In a particular illustrative embodiment, sequentially exposing the fluid to electromagnetic energy may be done by sequentially filtering the electromagnetic energy output from the plurality of lasers, using fiber grating filter 602 with a plurality of grating filters 603-605.

Referring now to the several non-limiting illustrative embodiments described above and shown in the figures, one skilled in the art with the benefit of the present disclosure will better understand several non-limiting operational examples. An optical absorption spectrum can be generated using single-pass and/or multiple-pass absorption spectroscopy to indicate the presence of one or more specified molecules in a fluid sample. Oil-based mud filtrate often has a distinct spectral signature due to the presence of olefins and esters, which do not naturally occur in crude oils. For example, olefins produce peaks in the mid-infrared region from about 800 cm⁻¹ to about 1000 cm⁻¹ and esters produce peaks from about 1,600 cm⁻¹ to about 1,800 cm⁻¹. In operation, the downhole spectrometer can be used to estimate the percentage of oil based mud filtrate contamination of crude oil samples as they are being collected downhole. One can continue withdrawing and discarding oil removed from the downhole formation until the contamination falls below a desired level and then diverts a clean fluid sample being withdrawn into a sample collection tank.

In some embodiments, a tool such as the spectrometer described above may be used for permanent well monitoring. In these embodiments, the spectrometer or at least a portion of the spectrometer may be installed within a producing well to monitor production of downhole fluids. In some cases, producing wells may produce harmful compounds and/or gasses that may cause damage to equipment or present hazards at a well site. In one example, the method includes monitoring a producing well to estimate production downhole fluid properties. The fluid properties may include the presence of harmful compounds such as hydrogen sulfide, carbonyl sulfide, cyanide, hydrogen cyanide, sulfur dioxide, and brine.

In at least one embodiment, one or more spectrometers or at least a portion of the spectrometers, as described and discussed above, may be used to periodically or continuously monitor production of downhole fluids. For example, one or more readings can be taken with at least one spectrometer every 30 seconds, minute, two minutes, 5 minutes, one-half hour, hour, two hours, or any periodic interval desired. In another example, at least one spectrometer can continually acquire data which can be processed in real time or stored and, if desired, later analyzed to provide a continuous monitoring of the production of downhole fluids as it is acquired.

In another embodiment an apparatus is disclosed for estimating a property of a downhole fluid, the apparatus including but not limited to a carrier that is conveyable in a borehole; a test cell carried by the carrier for capturing the downhole fluid; a rare earth doped electromagnetic energy source in electromagnetic energy communication with the downhole fluid in the test cell; and an electromagnetic energy detector in electromagnetic energy communication with electromagnetic energy emitted by the rare earth doped electromagnetic energy source that has interacted with the fluid for estimating the property of the downhole fluid. In another embodiment of the apparatus the electromagnetic energy detector is a photodetector and wherein the electromagnetic energy source is a rare earth doped laser selected from at least one of a rare earth doped fiber laser, a rare earth doped silicon on insulator laser and a quantum dot laser, the apparatus further includes but is not limited to an electromagnetic energy pump in optical communication with the rare earth doped electromagnetic energy source. In another embodiment of the apparatus the electromagnetic energy pump, rare earth doped laser and photo detector are located downhole, the apparatus further includes but is not limited to an electro optic modulator integrated into the rare earth doped laser for adjusting a frequency of electromagnetic energy emitted from the rare earth doped laser to a wavelength of interest for detecting the property of the downhole fluid. In another embodiment of the apparatus the electro optic modulator device is an integrated device is at least one of an integrated stress tuner and a thermal tuner and wherein the rare earth doped laser further comprises a plurality of rare earth doped lasers integrated on a silicon wafer with the electro optic modulator, wherein each of the plurality of rare earth doped lasers' frequency of electromagnetic energy output is tunable using the electro optic modulator.

In another embodiment of the apparatus the rare earth doped laser further comprises a nanocavity in a two-dimensional photonic crystal slab wherein a Q for the rare earth doped laser is higher than about 1000. In another embodiment of the apparatus the rare earth electromagnetic energy source is a surrounding medium refractive index (SRI) sensor immersed in the downhole fluid wherein electromagnetic energy from the electromagnetic energy source indicates an SRI of the downhole fluid, wherein the SRI for the downhole fluid is used in estimating the property of the fluid. In another embodiment of the apparatus the apparatus further includes but is not limited to an electromagnetic energy pump located outside of the test cell; a window formed in a side of the test cell for ingress and egress of electromagnetic energy to and from the test cell, wherein electromagnetic energy detector and the electromagnetic energy pump are located outside of the test cell and the electromagnetic energy source is located inside of the test cell, wherein the electromagnetic energy pump further comprises gratings, each of which reflect electromagnetic energy at a frequency of interest from electromagnetic energy that has interacted with the fluid, to detect a compound of interest in the fluid.

In another embodiment of the apparatus the electromagnetic energy that has interacted with the fluid is at least one of electromagnetic energy that has passed through the downhole fluid, electromagnetic energy that fluoresces from the downhole fluid and electromagnetic energy that has reflected off of the downhole fluid, wherein the electromagnetic energy source further comprises gratings, each of which reflect electromagnetic energy at a frequency of interest from electromagnetic energy that has interacted with the fluid, to detect a compound of interest in the fluid, the apparatus further includes but is not limited to a processor configured to analyze the electromagnetic energy that has interacted with the downhole fluid for transmittance, fluorescence, absorbance and reflectance.

In another embodiment, a method for estimating a property of a downhole fluid is disclosed, the method including but not limited to capturing a downhole fluid in a test cell; introducing electromagnetic energy from a rare earth doped electromagnetic energy source downhole into the downhole fluid in the test cell; and detecting electromagnetic energy emitted by the rare earth doped electromagnetic energy source that has interacted with the downhole fluid using an electromagnetic energy detector in electromagnetic energy communication with the downhole fluid for estimating the property of the downhole fluid. In another embodiment of the method the electromagnetic energy detector further comprises a photodetector and the rare earth dope electromagnetic energy source further comprises a rare earth doped laser that is selected from at least one of a rare earth doped fiber laser, a rare earth doped silicon on insulator laser and a quantum dot laser.

In another embodiment of the method the rare earth doped electromagnetic energy pump, rare earth doped laser and photo detector are down hole, the method further including but not limited to adjusting a frequency of the rare earth doped laser to a wavelength of interest using an electro optic modulator for detecting the presence of a chemical of interest in the fluid for estimating the property of the downhole fluid. In another embodiment of the method the electro optic modulator device is at least one of a piezoelectric stress tuner, a mechanical stress tuner and a thermal tuner. In another embodiment of the method the rare-earth doped laser further comprises a nanocavity in a two-dimensional photonic crystal slab wherein a Q for the rare-earth doped laser is higher than about 1000. In another embodiment of the method the rare earth doped electromagnetic energy source further comprises a fiber grating wherein electromagnetic energy from the fiber grating indicates a surrounding medium refractive index for the downhole fluid, wherein the surrounding medium refractive index for the downhole fluid is used in estimating the property of the downhole fluid. In another embodiment of the method, the method further includes but is not limited to sending electromagnetic energy into the test cell from an electromagnetic energy pump to the rare earth doped electromagnetic energy source through a window in the test cell, wherein the electromagnetic energy pump is located outside of the test cell.

In another embodiment of the method the electromagnetic energy that has interacted with the fluid is at least one of electromagnetic energy that has passed through the fluid and electromagnetic energy that has reflected off of the fluid, the method further includes but is not limited to analyzing the electromagnetic energy that has interacted with the fluid for at least one of transmittance, fluorescence, absorbance and reflectance; and estimating the property of the downhole fluid. In another embodiment, a method for estimating a property of a downhole fluid is disclosed, the method including but not limited to traversing a well bore using a carrier attached to a test cell; introducing a downhole fluid into the test cell; introducing electromagnetic energy from a rare earth doped electromagnetic energy source downhole into the downhole fluid in the test cell; and detecting electromagnetic energy that has interacted with the fluid with an electromagnetic energy source in electromagnetic communication with the downhole fluid for estimating the property of the downhole fluid. In another embodiment of the method the electromagnetic energy source further comprises a rare-earth doped laser that is one of a rare earth doped fiber laser, a rare earth doped silicon on insulator laser and a quantum dot laser. In another embodiment of the method at least two of the electromagnetic energy source, the rare earth doped laser and the photo detector are down hole, the method further including but not limited to adjusting a frequency of electromagnetic energy output from the electromagnetic energy source to a wavelength of interest using an electro optic modulator for estimating a property of the fluid. In another embodiment of the method the rare earth doped electromagnetic energy source further comprises a fiber grating wherein electromagnetic energy from the fiber grating indicates a surrounding medium refractive index for the downhole fluid, wherein the surrounding medium refractive index for the downhole fluid is used in estimating the property of the downhole fluid.

Having described above the several aspects of the disclosure, one skilled in the art will appreciate several particular embodiments useful in determining a property of an earth subsurface structure using a downhole spectrometer.

The present disclosure is to be taken as illustrative rather than as limiting the scope or nature of the claims below. Numerous modifications and variations will become apparent to those skilled in the art after studying the disclosure, including use of equivalent functional and/or structural substitutes for elements described herein, use of equivalent functional couplings for couplings described herein, and/or use of equivalent functional actions for actions described herein. Such insubstantial variations are to be considered within the scope of the claims below.

Given the above disclosure of general concepts and specific embodiments, the scope of protection is defined by the claims appended hereto. The issued claims are not to be taken as limiting Applicant's right to claim disclosed, but not yet literally claimed subject matter by way of one or more further applications including those filed pursuant to the laws of the United States and/or international treaty. 

What is claimed is:
 1. An apparatus for estimating a property of a downhole fluid, the apparatus comprising: a carrier that is conveyable in a borehole; a test cell carried by the carrier for capturing the downhole fluid; a rare earth doped electromagnetic energy source in electromagnetic energy communication with the downhole fluid in the test cell; and an electromagnetic energy detector in electromagnetic energy communication with electromagnetic energy emitted by the rare earth doped electromagnetic energy source that has interacted with the fluid for estimating the property of the downhole fluid.
 2. The apparatus of claim 1, wherein the electromagnetic energy detector is a photodetector and wherein the electromagnetic energy source is a rare earth doped laser selected from at least one of a rare earth doped fiber laser, a rare earth doped silicon on insulator laser and a quantum dot laser, the apparatus further comprising: an electromagnetic energy pump in optical communication with the rare earth doped electromagnetic energy source.
 3. The apparatus of claim 2, wherein the electromagnetic energy pump, rare earth doped laser and photo detector are located downhole, the apparatus further comprising: an electro optic modulator integrated into the rare earth doped laser for adjusting a frequency of electromagnetic energy emitted from the rare earth doped laser to a wavelength of interest for detecting the property of the downhole fluid.
 4. The apparatus of claim 3, wherein the electro optic modulator device is an integrated device is at least one of an integrated stress tuner and a thermal to and wherein the rare earth doped laser further comprises a plurality of rare earth doped lasers integrated on a silicon wafer with the electro optic modulator, wherein each of the plurality of rare earth doped lasers' frequency of electromagnetic energy output is tunable using the electro optic modulator.
 5. The apparatus of claim 2, wherein the rare earth doped laser further comprises a nanocavity in a two-dimensional photonic crystal slab wherein a Q for the rare earth doped laser is higher than about
 1000. 6. The apparatus of claim 1, wherein the rare earth electromagnetic energy source is a surrounding medium refractive index (SRI) sensor immersed in the downhole fluid wherein electromagnetic energy from the electromagnetic energy source indicates an SRI of the downhole fluid, wherein the SRI for the downhole fluid is used in estimating the property of the fluid.
 7. The apparatus of claim 1, the apparatus further comprising: an electromagnetic energy pump located outside of the test cell; a window formed in a side of the test cell for ingress and egress of electromagnetic energy to and from the test cell, wherein electromagnetic energy detector and the electromagnetic energy pump are located outside of the test cell and the electromagnetic energy source is located inside of the test cell, wherein the electromagnetic energy pump further comprises gratings, each of which reflect electromagnetic energy at a frequency of interest from electromagnetic energy that has interacted with the fluid, to detect a compound of interest in the fluid.
 8. The apparatus of claim 1, wherein the electromagnetic energy that has interacted with the fluid is at least one of electromagnetic energy that has passed through the downhole fluid, electromagnetic energy that fluoresces from the downhole fluid and electromagnetic energy that has reflected off of the downhole fluid, wherein the electromagnetic energy source further comprises gratings, each of which reflect electromagnetic energy at a frequency of interest from electromagnetic energy that has interacted with the fluid, to detect a compound of interest in the fluid, the apparatus further comprising: a processor configured to analyze the electromagnetic energy that has interacted with the downhole fluid for transmittance, fluorescence, absorbance and reflectance.
 9. A method for estimating a property of a downhole fluid, the method comprising: capturing a downhole fluid in a test cell; introducing electromagnetic energy from a rare earth doped electromagnetic energy source downhole into the downhole fluid in the test cell; and detecting electromagnetic energy emitted by the rare earth doped electromagnetic energy source that has interacted with the downhole fluid using an electromagnetic energy detector in electromagnetic energy communication with the downhole fluid for estimating the property of the downhole fluid.
 10. The method of claim 9, wherein the electromagnetic energy detector further comprises a photodetector and the rare earth dope electromagnetic energy source further comprises a rare earth doped laser that is selected from at least one of a rare earth doped fiber laser, a rare earth doped silicon on insulator laser and a quantum dot laser.
 11. The method of claim 10, wherein the rare earth doped electromagnetic energy pump, rare earth doped laser and photo detector are down hole, the method further comprising: adjusting a frequency of the rare earth doped laser to a wavelength of interest using an electro optic modulator for detecting the presence of a chemical of interest in the fluid for estimating the property of the downhole fluid.
 12. The method of claim 11, wherein the electro optic modulator device is at least one of a piezoelectric stress tuner, a mechanical stress tuner and a thermal tuner.
 13. The method of claim 10, wherein the rare-earth doped laser further comprises a nanocavity in a two-dimensional photonic crystal slab wherein a Q for the rare-earth doped laser is higher than about
 1000. 14. The method of claim 10, wherein the rare earth doped electromagnetic energy source further comprises a fiber grating wherein electromagnetic energy from the fiber grating indicates a surrounding medium refractive index for the downhole fluid, wherein the surrounding medium refractive index for the downhole fluid is used in estimating the property of the downhole fluid.
 15. The method of claim 10, the method further comprising: sending electromagnetic energy into the test cell from an electromagnetic energy pump to the rare earth doped electromagnetic energy source through a window in the test cell, wherein the electromagnetic energy pump is located outside of the test cell.
 16. The method of claim 10, wherein the electromagnetic energy that has interacted with the fluid is at least one of electromagnetic energy that has passed through the fluid and electromagnetic energy that has reflected off of the fluid, the method further comprising: analyzing the electromagnetic energy that has interacted with the fluid for at least one of transmittance, fluorescence, absorbance and reflectance; and estimating the property of the downhole fluid.
 17. A method for estimating a property of a downhole fluid, the method comprising: traversing a well bore using a carrier attached to a test cell; introducing a downhole fluid into the test cell; introducing electromagnetic energy from a rare earth doped electromagnetic energy source downhole into the downhole fluid in the test cell; and detecting electromagnetic energy that has interacted with the fluid with an electromagnetic energy source in electromagnetic communication with the downhole fluid for estimating the property of the downhole fluid.
 18. The method of claim 17, wherein the electromagnetic energy source further comprises a rare-earth doped laser that is one of a rare earth doped fiber laser, a rare earth doped silicon on insulator laser and a quantum dot laser.
 19. The method of claim 18, wherein at least two of the electromagnetic energy source, the rare earth doped laser and the photo detector are down hole, the method further comprising: adjusting a frequency of electromagnetic energy output from the electromagnetic energy source to a wavelength of interest using an electro optic modulator for estimating a property of the fluid.
 20. The method of claim 19, wherein the rare earth doped electromagnetic energy source further comprises a fiber grating wherein electromagnetic energy from the fiber grating indicates a surrounding medium refractive index for the downhole fluid, wherein the surrounding medium refractive index for the downhole fluid is used in estimating the property of the downhole fluid. 